54 y M presents to the ED with complaints of chest pain starting acutely 4 hours ago. The EKG is as follows:
What’s the diagnosis?
Posterior MI. Which is suggested by the following findings in leads V1-3:
- Horizontal ST depression
- Tall, broad R waves (>30ms)
- Upright T waves
- Dominant R wave (R/S ratio > 1) in V2
On EKG, because the electrical activity from the posterior portion of the myocardium is recorded from the anterior side the standard injury pattern becomes inverted. Q waves become R waves, ST elevation becomes ST depression, and terminal T waves become upright. In this case you would order a posterior EKG and look for ST elevation >0.5mm in leads V7-9 to diagnose posterior MI. In this case the posterior EKG would look something like this:
Interesting facts about posterior MI and why it is important to be vigilant:
- Posterior infarction accompanies 15-20% of STEMIs – usually occurring in association with an inferior or lateral infarction.
- Isolated posterior MI occurs in about 3-11% of all MIs.
- Posterior extension of an inferior or lateral infarct implies a much larger area of myocardial damage and increased risk of cardiac dysfunction and death.
- Isolated posterior infarction is an indication for emergent coronary reperfusion, but the lack of obvious ST elevation often leads to missed diagnosis.